The invention relates to delivery, administration or injection of a substance through a needle, conduit ir the like. More particularly, it relates to an injection needle for injection into body tissue, preferably into or through the human skin, which injection needle is flexible in the inserted state and conveys a fluid to be administered into the tissue. The injection needle preferably forms an inner channel through which the fluid is conveyed, i.e. it preferably forms an injection cannula.
In a great many therapeutic or diagnostic applications it is necessary for an injection needle to be placed in or lodged in body tissue over quite a long period of time, for example in order to permit repeated or sustained administration of therapeutic or diagnostic fluids. In the treatment of patients with diabetes, for example, insulin is administered at regular intervals through an injection needle which remains in the patient's body tissue over a period of several days.
For this purpose, it is known from U.S. Pat. No. 4,562,751, for example, to use an injection needle made of steel. A steel needle does have a simple structure, but it also has various disadvantages. The sharp needle tip of the rigid injection needle can cause constant irritation of the surrounding tissue since it cannot adapt to the movements of the tissue. Such a rigid injection needle, when inserted, is uncomfortable for the patient and even painful. There is also a considerable risk of needlestick injuries to the tissue surrounding the needle tip and also when removing the injection needle from the tissue.
Devices referred to as soft cannulas and which are flexible have therefore been developed. U.S. Pat. No. 4,755,173, for example, describes an injection set used for subcutaneous administration of a fluid, in which a steel needle is guided through a soft cannula so that the sharp tip of the steel needle protrudes from the soft cannula. With the aid of the steel needle, the soft cannula is inserted into body tissue. The steel needle is then removed from the soft cannula, as a result of which a fluid connection is established between the soft cannula and the tissue.
A soft cannula of this kind can easily follow the movements of the tissue, so that there is no irritation, or only slight irritation, of the surrounding tissue. To insert the soft cannula, however, it is still necessary to use a rigid injection needle, for example a steel needle, which has to be removed after the soft cannula described has been inserted. The soft cannula therefore also poses the risk of a needlestick injury. In addition, the opening through which the steel needle has been removed has to be sealed off to permit correct use of the injection needle. This procedure is complicated and increases the risk of a lack of leaktightness when fitting the cannula.